The present invention concerns a water heater—in particular a boiler—comprising an apparatus for the physical treatment of drinking water for reducing calcification, wherein the apparatus has at least one water inlet and at least one water outlet.
PCT application WO 99/48822 describes that a weakly acid ion exchanger resin in the Ca-form catalytically triggers at its surface lime precipitation from a lime-bearing solution. That process can be used for physical water treatment: the lime seed crystals formed at the surface of the catalytically acting granular material are easily detached from the surface and are crystallisation centers in the supersaturated water itself. The growth of those crystallisation centers binds the excess calcium and carbonate ions to themselves and in that way precipitation processes on pipe and boiler walls are lastingly suppressed. PCT application WO 99/48822 also contains technical descriptions of how preferably water treatment apparatuses with that catalyst material are designed and used in a drinking water installation. Essentially those water treatment apparatuses are made up of a pressure-resistant container, a nozzle plate and a granular material-retaining filter element. The original idea was to install that catalyst technology in the cold water line of the drinking water installation.
It was subsequently found that this catalyst granular material is most effectively used in the hot water region in combination with a hot water storage unit, more specifically for the following reasons:                The degree of supersaturation of the lime-bearing water is higher in the hot water region; in a corresponding manner the probability of seed crystals forming at the surface of the catalyst granular material also increases.        The growth kinetics of the lime seed crystals formed are substantially faster at higher temperatures; in other words, lime seed crystals formed are available more quickly as crystallisation centers.        In drinking water heating systems with storage unit the water involved has a markedly longer mean residence time in the system. That residence time permits a longer water treatment time. That permits efficient water treatment even with small compact catalyst units.        With warm or hot water the catalyst granular material can be ideally disinfected; disinfecting is desirable for safe operation in the drinking water sector by virtue of the large surface area of the material involved, from the hygiene point of view.        
Those reasons led to the catalyst granular material preferably being used in the hot water region. In order to ensure protection for the entire drinking Water heating system, it is necessary for all the hot water to be brought into contact with the catalyst. That requirement is satisfied for example if the water treatment apparatus is either used in an existing circulation conduit and the hot water is circulated with a circulation pump or alternatively its own bypass conduit is built by way of the hot water storage unit and the water treatment apparatus is integrated into that conduit together with a circulation pump.
Austrian patent specification AT 406 826B in FIG. 2 thereof shows an embodiment for the use of the catalyst granular material in the hot water circulation. That specification shows an apparatus for disinfecting a water treatment unit, which is installed as an independent device in the cold water part or the hot water part of a drinking water installation. The incorporation of such an additional device gives rise to additional expenditure and requires a greater amount of space. In addition that additional device requires a power supply for heating the water to be treated. That gives rise to an additional energy consumption which cannot be completely recovered by the heat losses which occur, in the drinking water installation.
The technical solution with a circulation conduit has two crucial disadvantages:                the system needs a circulation conduit with a circulation pump and power for operation thereof, and        there are heat losses due to the circulation.        
Those disadvantages disturb the otherwise impeccable ecological and economic balance sheet of the catalyst technology. The process itself of forming the seed crystals does not need any chemical additives—it is a ‘chemical-free’ process—and no energy as the energy necessary for formation is stored in the supersaturation of the lime-bearing aqueous solution. The subsequent installation of a circulation conduit with a circulation pump increases the level of capital investment expenditure and operation of the circulation gives rise to operating costs. Particularly in the case of small installations, those circumstances have a particularly disadvantageous effect on the decision on the part of a customer for adopting that technology. Furthermore, when using layer-type storage arrangements, circulation by way of the storage unit gives rise to problems.
It is also known for the water-treating substance, preferably the catalyst granular material, to be integrated in a technical fluid-filled installation directly into the region where for example the lime problems occur. The technical installation itself is routinely provided not solely for receiving the water-treating substance, preferably the catalyst granular material, and performs another, technically necessary purpose. This can be for example the supply (storage/buffering) of a fluid, in particular the storage of hot water (energy storage) for later consumption. The technical installations described can also serve for heating fluids, passing the fluid along, or a combination of the stated functions.
It is assumed in this respect that transport, which is necessary for the treatment, of the fluid to the catalyst granular material and transport of the crystallisation centers which are necessary for the water treatment from the surface of the catalyst granular material into the entire fluid-filled space is effected to a sufficient degree by means of diffusion and convection. Diffusion and convection however are generally very slow processes and it is not always possible to guarantee an adequate treatment efficiency in the entire fluid-filled space. In addition specific adaptation of the listed embodiments in order to permit diffusion and convection to an adequate degree in the respective use sometimes requires a high level of technical expenditure which again nullifies a part of the savings (no pressure vessel, no heating means).